From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page discussing magnetisation, the use of soft iron keepers, and the effects of tapering magnet pole ends on tractive effort for a magneto.
| Identifier | ExFiles\Box 35\1\ scan 180 | |
| Date | 11th August 1920 | |
| -10- Contd. R.R. 259a/100T.(S H.{Arthur M. Hanbury - Head Complaints} 159, 11-8-20) G 2600 would seem to draw the magnetisation to the sides and bottom of the magnet rather than to the faces to which the pole pieces abut. If a soft iron keeper were made to fit in the space between the poles in the same way as the armature and pole pieces do, and we wound this with a coil and used an electric current, and subjected the magnet to shocks, while under its influence the actual magnetisation produced in the magnet might quite conceivably be more nearly what is required in practice. It would then be probably undesirable to use any other form of keeper, owing to the distortion such would tend to produce in the magnetisation. We would like to point out that the traction a magnet will exert on a piece of soft iron is not really a measure of the practically useful flux. A magnet rigidly magnetised (if possible) by the above suggested method would not support so much weight and yet would be better for a magneto. Again, the same magnet will exert a larger tractive effort if its pole ends are tapered off to some extent. This seems at first sight wrong, but nevertheless it is a fact that the same flux crowed across a smaller area, exerts a greater magnetic pull. Provided we do not taper the pole ends down to such an extent as to reduce the flux appreciably, we actually get a greater weight supported. EFC. | ||